The present invention relates to method and apparatus for controlling the ignition timing of an internal combustion engine, and more particularly to method and apparatus for controlling the ignition timing of an internal combustion engine by detecting the occurrence of knocking.
The occurrence of knocking in an internal combustion engine creates an unpleasant sensation to the driver because of knocking noise and results in a decrease of engine output due to the generation of counter-torque or the braking of the engine due to overheating of the engine. The knocking has a close relation with ignition timing of the engine, and it has been known that a maximum engine output is obtainable by establishing the ignition timing or ignition advance angle to a point immediately before the knocking point in view of the characteristic of the engine. The selection of a small ignition advance angle to avoid the occurrence of knocking leads to a reduction of engine output and hence it is desired to set the ignition timing to the point immediately before the knocking point.
U.S. Pat. No. 4,002,155 discloses a method for controlling the ignition timing in which the ignition advance angle is retarded when the occurrence of knocking is detected and then the ignition advance angle is gradually advanced, and when the knocking again occurs during the process of advancing the angle, the ignition advance angle is again retarded, and the above step is repeated.
In the disclosed control method, the ignition timing is always advanced toward the advance angle and when the knocking occurs, the angle is retarded. Accordingly, the engine torque varies depending on the frequency of knocking and the variation of torque adversely affects the operability of the engine. If the magnitude of the angle to be retarded when knocking occurs is selected to be small to minimize the effect, knocking cannot be rapidly stopped and hence the disadvantages resulting from the knocking cannot be fully eliminated.